Several studies had shown that younger breast cancers often exhibited more aggressive biological characteristics, such as estrogen receptor-negative (ER–) and HER2 positive tumor, high grade and are more prone to lymph node metastasis, resulting in higher recurrence and mortality rates.[10–14] Thus, in this study, we used an age cutoff of 40 years to perform the relationship between age and prognosis in her2 positive breast cancer patients. The gene discussed is ESR1; the disease is breast cancer.